MicroRNAs (miRNAs) play important roles in the the gene regulation of carcinogenesis including breast cancer. miR‑519d has been studied in various types of cancer, but its role in breast cancer remains unclear. In the present study, we investigated the expression and biological function of miR-519d in breast cancer. Using quantitative RT-PCR (RT-qPCR) analysis, we analyzed the expression of miR-519d in breast cancer tissues and cell lines. It was shown that miR-519d expression was decreased in cancer tissues and cell lines compared with their controls. Overexpression of miR-519d inhibited cell proliferation and invasion, and induced apoptosis of breast cancer cells. Signal transducer and activator of transcription 3 (STAT3) was predicted as a target gene of miR-519d and it was verified by the luciferase reporter assay. Additionally, STAT3 mRNA and protein expression levels were downregulated in the cells with miR-519d overexpression as determined by RT-qPCR and western blotting. Taken together, the results indicated that miR-519d functions as a tumor suppressor in breast cancer by suppressing STAT3 expression.